Geokon 8020-42, Руководство по установке, Страница: 5 / 13

1
LPF
φ
1
φ
2
VCO
Instrumentation
Amplifier
and
Schmitt Trigger
Phase Comparator
Output Buffer
VW Gage
Coil
Microprocessor
V+
1. INTRODUCTION
The Geokon 8020-42 Single Coil Autoresonant Adapter (SCA) is a device that allows single coil
vibrating wire gages to be driven in the “Autoresonant” mode, instead of the standard “Pluck and
Read” mode. The benefits of Autoresonant vs. Pluck and Read topologies are many, including
greater reading stability and wider dynamic bandwidth. In addition, since there is no
asynchronous swept frequency or pulse pluck excitation to interfere with the vibrating wire
signal, there is the ability to read the gage frequency with a general-purpose frequency counter or
low cost datalogger, instead of a complex dedicated readout device or datalogger.
Historically, autoresonant vibrating wire gages have employed two coils. The first is the
Transmit (excitation) coil that provides a phase synchronous pulse (pluck) to maintain
oscillation, while the second is the Receive (reading) coil that recovers the vibrating wire signal.
The two-coil approach, while dependable, adds considerably to the cost and imposes a
considerable mechanical limitation to the design and construction of the gage. Since the SCA is
designed to operate as a “transceiver” using only one coil, these limitations are eliminated while
providing the benefits of the autoresonant mode.
Figure 1 - Block Diagram
Frequency
Output
Enable
PLL_OUT
VCO_HOLD
T/R
Switch